Various industrial installations include pipelines containing valves at locations which are inaccessible, or accessible only with difficulty, or are within hazardous environments. Therefore, servicing or replacement of such valves is a difficult and time-consuming operation and could require maintenance personnel to be exposed to radiation or other hazards. Frequently, it will be necessary to completely shut-down a portion of the installation which is associated with the valve and the duration of the shut down depends on the time required to complete servicing of the valve.